Thesis (M.Sc.). / Written for the Dept. of Biology. Title from title page of PDF (viewed 2009/07/02). Includes bibliographical references.

Please read the abstract in the section 00front of this document / Thesis (PhD(Food Science))--University of Pretoria, 2005. / Food Science / unrestricted

The Nile perch, Lates niloticus (Linnaeus, 1758), is a predacious freshwater fish widely distributed throughout the Afro-tropic eco-zone. The species was introduced to Lake Victoria in the early 1950s and by 1980 it had dominated the fisheries of Lake Victoria. This was followed by a dramatic decrease in the Nile perch fisheries production due to uncontrolled exploitation. The purpose of this thesis is to provide fundamental knowledge that can be applied in aquaculture and fisheries management through the study of the reproductive biology of L. niloticus. The research was aimed at the studying of the diverse aspects of the reproductive biology of L. niloticus in the Lake Victoria, Ugandan populations. This included reproductive patterns in relation to proximate environmental conditions, size at sexual maturity, gonad and gamete structure, gametogenesis and induced ovulation. The size at 50% sexual maturity for female Nile perch was 59.4 cm, which is lower than the earlier reported size of greater than 90 cm total length. Male L. niloticus matured at 57.8 cm total length in Lake Victoria. Microscopy revealed that L. niloticus from Lake Victoria had one spawning period that started in November and ended in March. Type I atresia occurred at high frequency from March to June, and type III atresia was present from July to September and between November and December. Spermatogenesis in L. niloticus is cystic and sperm development is the result of asynchronous activation of the germ cells. Type II spermatozoa are simple, uni-flagellate aquasperm with no acrosome. Oogenesis in L. niloticus differed from that of other fishes in that no cortical alveoli were present in any stage of oogenesis. Numerous oil globules were present in the primary yolk vesicle stage. This formed one centrally positioned, large oil globule in the tertiary yolk vesicle oocytes during final oocyte maturation. Clove oil was an effective sedative and an anaesthetic for the handling of L. niloticus. Induction time was more rapid at clove oil concentrations of 50 - 100 μl L⁻¹ than in fish exposed to clove oil concentrations less than 50 μl L⁻¹. Fish exposed to high concentrations exhibited significantly short induction times of less than 240 seconds. On average, fish recovered within 673 ± 58 seconds for all the concentrations used. Prolonged exposure of L. niloticus to low clove oil concentrations of 2.5 - 10 μl L⁻¹ did not change the blood plasma cortisol, glucose, and the lactate and chloride ion concentration, relative to the control treatment. Captive breeding was attempted by conducting induced spawning experiments. Only final oocyte maturation was achieved using a decapeptide Gonadotropin Releasing Hormone (Dargin, sGnRH-MET), combined with a water-soluble dopamine receptor antagonist metoclopramide. This thesis suggests a research approach that provides a basis for aquaculture of the new species by first studying reproductive biology patterns and then linking the information to gonad and gamete structure so that spawning times can be estimated. It further provides insights into aspects of the reproductive biology of the species and the effects of hormonal intervention on oocytes by showing at which stage of oocyte development hormones should be applied in L. niloticus. Clove oil can be used to sedate and anaesthetise L. niloticus broodfish to reduce the stress related to the handling of large specimens.

This doctoral thesis examines the challenges to co-management in the Tanzania part of Lake Victoria. The study mainly addresses the Nile perch fishery and uses the fishing communities of Bukoba Rural district, Tanzania as a case study. Co-management in Lake Victoria is defined as the sharing of the management responsibilities between the state and the fishing communities. Co-management was adopted in the Lake Victoria fisheries on the understanding that it has the capacity to provide space in which the poor resource users could be empowered to sustainably manage their resource base. The assumption was that the sharing of the management responsibilities between the state and the community of users would have led to equity in resource access, poverty reduction and resource sustainability. Thus, reducing the role of the state and enhancing that of the communities was seen as a solution to the problems of poverty and illegal fishing that are threatening the sustainability of the fishery and the fishers dependent on it. However, in spite of these proclaimed efforts, illegal fishing and poverty in Lake Victoria remain major threats to the long-term sustainability of the fishery, a fact that is raising questions on the efficacy of co-management in Lake Victoria. These questions have particularly focused on the co-management model and the neo-liberal ideals that underlie it, namely decentralization, participation and accountability. The central argument in this thesis, however, is that co-management performance in Lake Victoria is to a large extent shaped by the complex international, national, and local context in which it is implemented and which in turn shapes the problems of poverty and illegal fishing that co-management is supposed to address. The study concludes that the international and national politics behind the Nile perch fishery intersect with the cultural and social context in which the fishery is embedded to shape co-management performance at the local level. For analysis, the study applies a multi-level approach and draws insights from the common pool resources theory, the actor-oriented approach, the entitlement framework, and the theory of the state. Detailed interviews across scale, secondary data, policy documents, and laws, supported by quantitative data are the methods applied.